It is known to provide a row-crop harvesting machine, as for example a corn cutter, with a position-detecting system that is connected to the steering system of the agricultural machine so as automatically to guide this machine accurately along the rows of crop. The function of this position-detecting system is to ensure that each of the rows of crop passes directly into a respective throat of a respective cutter of the crop head of the machine. Normally such a machine has a plurality of forwardly extending arms that define a plurality of throats equispaced apart in a direction transverse to the normal transport direction of the machine along the ground.
One such position-detecting system is seen in German Patent Publication No. 2,434,396 which is based on a relatively complex computer that is connected to a pair of sensors each of which bears on a respective side of a single row of the crop entering the harvesting machine. Such a system is relatively expensive because it is necessary to provide a relatively complex minicomputer for reducing the readings of the feelers to usable information. Furthermore if the single row of crop being sensed is irregular or one of the two feelers fails, the entire system is down and must be repaired. This last-mentioned disadvantage can be overcome by providing a plurality of such row feelers; however, the overall cost of such a position-detecting system becomes prohibitive.
In this known system a blocking of the cutter throat of the harvesting machine at the position detector also will give a false reading. What is more, the feelers are normally set up so that if for some reason the agricultural machine in question must be backed up, a considerable danger of damaging the feelers by bending them over is present. Finally, this known system makes it very difficult to use the machine on anything but a perfectly regularly spaced row crop. Any variation in the row spacing requires extensive re-alignment and re-setting of the entire machine, even though the normal crop cutter is set up so that its throat can accept crops at a row spacing within the normal range without requiring re-adjustment of the machine.